1. Field of the Invention
The present invention relates to the art of wire feeding mechanisms and, more particularly, to drive rollers used in wire feeding mechanisms for driveably advancing a welding wire. The present invention finds particular application in conjunction with drive rollers used to advance a welding wire and will be described with particular reference thereto. It is to be appreciated, however, that the present invention may relate to other similar environments and applications.
2. Discussion of the Art
U.S. Pat. No. 6,557,742 to Bobeczko et al., U.S. Pat. No. 5,816,466 to Seufer and U.S. Pat. No. 4,235,362 to Hubenko, all expressly incorporated herein by reference, disclose wire feeding mechanisms and provide general background information related thereto.
Wire feeding mechanisms that move consumable electrode wire from a supply reel to a welding gun are generally well known. For example, Seufer discloses a wire feed mechanism having a wire pathway through which a continuous length of wire is advanced. Typically, wire feed mechanisms include motor-driven drive rolls that engage diametrically opposite sides of a wire to move the wire along a path through a housing of the feeding mechanism. Once through the housing, the wire is moved through a flexible tube or conduit leading to a welding gun. Often, the conduit also carries shielding gas and electrical current to the welding gun.
Typically, each of the drive rollers is mounted on a roller support and all of the roller supports are driveably engaged with one another. Thus, powered rotation of a single roller support causes rotation of all the roller supports and the drive rollers supported thereon. Usually, the drive rolls are a single pair of opposed rollers or a double pair of opposed rollers spaced apart along the wire path. In either arrangement, the drive rollers have an upstream side at which the wire enters the drive rollers and a downstream side at which the wire exits the driver rollers. On the upstream side, the wire is guided through an upstream tube toward a bite created between the drive rollers adjacent the upstream side. Likewise, on the downstream side, the wire exits the drive rollers and is guided through a downstream tube adjacent the downstream side. If a double pair of opposed rollers are used, another tube can be provided between the pairs of drive rollers to further guide the wire.
To impart an advancing force or motion to the wire, opposing drive rollers are positioned sufficiently close to one another so that the wire extending along the pathway is compressed between the opposing rollers. The compressive force in combination with friction between the material of the wire and the rollers advances the continuous length of wire along the wire path in a generally smooth and continuous manner. In some arrangements, one or more of the drive rollers are urged toward the wire by a biasing member to further impart an advancing force or motion on the wire.
The wire passing through the drive rollers has a generally round cross-section and is engaged tangentially by opposing, flat-faced drive rollers mounted transversely to the wire. As a result of this arrangement, the compressive forces exerted on the wire by the driver rollers often cause the wire to undesirably deform. The material characteristics of the wire largely determine the magnitude or amount the wire is deformed as a result of the compressive forces. Accordingly, a wire made from a material having a relatively high compressive yield strength, such as steel, will be deformed less than a wire made from a material having a moderate compressive yield strength, such as aluminum.
In some applications, one or both of each pair of drive rollers include U-shaped or V-shaped grooves extending circumferentially thereabout for reducing the deformation of the wire from the compressive forces of the drive rollers. When such grooves are employed, the wire is engaged by side walls of the drive roller forming the groove. As a result, the compressive force exerted by the drive roller with a groove tends to act and deform the wire along more of the wire's outer surface than if no groove was provided. More contact between the drive roller and the wire results in less deformation.
When grooves are used, they are typically employed in one of two arrangements. In one arrangement, with reference to FIG. 4, a pair of relatively shallow angled grooves 100,102 are provided on opposed drive rollers 104,106. More particularly, the first groove 100 in the first drive roller 104 is defined by side walls 108,110 which are at an angle of ninety degrees (90°) relative to one another. Likewise, the second groove 102 in the second drive roller 106 is defined by side walls 112,114 which are at an angle of ninety degrees (90°) relative to one another. Since both grooves 100,102 are configured alike, the drive rollers 104,106 grip wire 116 with an equal amount of force. A centerline of the wire 116 is generally centered between the drive rollers 104,106.
In the other arrangement, with reference to FIG. 5, a relatively sharp-angled groove 120 is provided in a first drive roller 122 and no groove is provided in a second, opposite drive roller 124. The groove 120 is defined by side walls 126,128 in the first drive roller 122 which are at an angle of between thirty and sixty degrees (30°-60°) and, preferably, an angle of sixty degrees (60°). The second drive roller 124, also referred to as a flat idler roller, has a flat surface 130 for engaging wire 132. A centerline of the wire 132 often sits below flat surface 134 of the first drive roller 122 which is the surface in which the groove 120 is formed. More particularly, the flat idler roller 124 pushes the wire 132 into the groove 120 which in turn propels the wire 132.
While these types of groove arrangements tend to lessen the amount a wire is deformed, the amount of compressive force required to input motion to the wire remains high. Reductions in the required compressive force are generally considered desirable and can decrease wear on the wire feed mechanism and/or reduce slippage of the wire relative to the drive rollers. Accordingly, any improvements to the drive rollers that decreases the required compressive force needed to drive the wire engaged by the drive rollers is deemed desirable.